1. Field of the Invention
The present invention relates to an organic EL circuit including, corresponding to each of a plurality of pixels, a plurality of driving transistors switched on and off in accordance data from a plurality of data lines and a plurality of EL elements corresponding to the plurality of driving transistors.
2. Description of the Related Art
Conventionally, use of an organic EL panel as a flat panel display is known. Because each pixel in an organic EL panel is self-emitting, an organic EL panel has advantages including that, unlike a liquid crystal display, no backlight is required and that the display is relatively bright.
FIG. 6 shows a structural example of a pixel circuit in a conventional organic El panel employing a thin film transistor (TFT). An organic EL panel is constructed by arranging elements such as these in a matrix form.
A gate line which extends in the row direction is connected to the gate of a scan TFT1 which is an n channel thin film transistor selected by the gate line. The drain of the scan TFT1 is connected to a data line which extends in the column direction, and the source of the scan TFT1 is connected to a storage capacitor SC, the other terminal of which is connected to a storage capacitance power source line VSC. The connection point between the source of the scan TFT1 and the storage capacitor SC is also connected to the gate of a driving TFT2 which is a p channel thin film transistor. The source of the driving TFT2 is connected to a power source PVDD and the drain of the driving TFT2 is connected to an organic EL element EL. The other terminal of the organic EL element EL is connected to a cathode power source VC.
When the gate line of the above circuit is at H level, the scan TFT1 is switched on, and the data in the data line at that point of time is stored in the storage capacitor SC. According to the data (electric potential) maintained in the storage capacitor SC, the driving TFT2 is switched on and off. When the driving TFT2 is switched on, an electric current flows through the organic EL element EL and light is emitted.
The data lines are sequentially switched on at a timing at which corresponding data is supplied to the video signal line. Therefore, the brightness of the organic EL element EL is controlled based on the video signal supplied to the data line. In other words, the gray scale display of each pixel is effected by controlling the gate potential of the driving TFT2, to control the electric current flowing through the organic EL element.
However, because there is an intrinsic difference in the threshold voltage (Vth) of the driving TFT2 for each pixel, the display of each pixel will not be equal, and, thus, the display will be uneven.